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Area forecast discussion
National Weather Service Buffalo New York
629 am EDT Sat Oct 21 2017

Synopsis...
high pressure will remain anchored along the mid-Atlantic coastline
this weekend with dry weather and well above normal temperatures
continuing. The pattern will then become more unsettled early next
week with a slow moving cold front bringing rain, followed by cooler
temperatures.

&&

Near term /through tonight/...
simply put...expansive ridging at all levels will continue to
dominate our weather through this period. High clouds will increase
this afternoon, but these will be thin enough for some sunshine to
make it through. Highs today be in the 70s which is 15 to 20 degrees
above normal. Enjoy!

For tonight, there will continue to be a modest southerly flow which
will limit radiational cooling across the lake plains where this
tends to result in downsloping. Temperatures will still drop off
nicely in the sheltered interior valleys with lows in the upper 40s.
Elsewhere lows will be in the lower to mid 50s.

&&

Short term /Sunday through Tuesday/...
Sunday and Sunday night our warm, pleasant autumn weather will
continue...as abundant daytime sunshine and dry conditions persist.
With 850 hpa temperatures remaining near +12-14c, afternoon
temperatures at the surface should top out in the 70s, and possibly
a spot 80f reading or two. A light southerly flow Sunday night, and
increasing cirrus will maintain mild conditions with overnight lows
in the mid 50s to lower 60s.

The better part of Monday should shape up nice, especially from the
Genesee Valley eastward which should remain dry.

This morning a deep upper level trough of low pressure is found on
water vapor imagery is found over The Rockies. Deep tropical
moisture is seen streaming northward from convection over the Gulf
of Mexico. A Pacific shortwave raced across Arizona this
morning...and will eventually leave a pv lobe over the Southern
Plains on Monday. Meanwhile a second Pacific shortwave will deepen a
trough over The Rockies and northern plains Monday, with a fair
amount of cooler air behind it. As this trough merges with the
lingering pv lobe over the Southern Plains Monday and Monday night
it will form a surface low Monday night over the Ohio Valley. It
still remains uncertain if the stronger forcing mechanisms will be
with this first shortwave or the second...but regardless a soon to
be negatively tilted upper level trough will form over the Great
Lakes. Cool air building in from the west will tighten a baroclinic
zone over the eastern Great Lakes Monday night and into
Tuesday...forming an axis that will support moderate to heavy rain.

For the rain timing, showers will reach portions of wny through the
afternoon Monday, with rain becoming more widespread Monday night as
the first Pacific shortwave (pv lobe over the southern plains) lifts
northward across the County Warning Area. An upper level jet will be
strengthening...to the tune of 130 knots, with our region found in
the right entrance region. This will create additional lift, that
when coupled with mid level lift ahead of the shortwave that will be
interacting with +2 South Dakota precipitable water (around 1.5 inches) widespread rain is
expected to form across wny later in the night. The amplified pattern
will create slow eastward movement to the rain...such that chance
pops will hold on through the night for much of the north country.

Tuesday a deep longwave trough will be closing off...and negatively
tilted over the Great Lakes and lower Ohio Valley. Southerly flow of
rich moisture will feed occasional rain through the day...that again
may be moderate to heavy. The duration of the event, coupled with
deeper moisture feeding the intensity of the rain suggests that an
inch or two of rain is reasonable at this point for this event.
Relatively dry ground should be able to absorb much of this rain,
with small creeks and streams swelling to bankfull. Given the deep
southerly flow, training embedded convection could pose a localized
flooding problem...but tough to pin down where this would be at this
point in time.

There will be several surface waves along this frontal zone passing
across the country...with a deepening surface low likely passing
near our region Tuesday. The track of the low is still with much
uncertainty...possibly tracking either just to our north, or south.
If the northward track pans out, Tuesday could feature some moderate
wind gusts.

Highs Tuesday will be in the lower 60s to the west, while mid to
upper 60s will occur towards the east.

&&

Long term /Tuesday night through Friday/...
as we push through Tuesday night...a dry slot should work across our
region within the occluded system. This will taper off the steady
rain to scattered showers from west to east...possibly completely
ending for a time over the western counties.

While the filling upper low will start to work its way across the
lower Great Lakes on Wednesday...surface based ridging and a lack of
moisture in the mid levels will limit the extent of any showers
activity. The showers that we do develop should be most prevalent
over the far western counties where deeper moisture will be
available to interact with increasing lake instability. The lake
effect rain showers could become more widespread east of both lakes
Wednesday night when the most unstable conditions and sufficient
synoptic moisture will be in place over the lakes. It will also be
much chillier...as 850 mb temps around zero c will only support
Wednesday afternoon temps that will range from the lower 50s in the
west to the mid to upper 50s east of the Genesee Valley. While this
will indeed by much cooler than the preceding week...these
temperatures will actually be close to where we should be for late
October.

Ridging is forecast to become established over the western counties
on Thursday...but the operational European model (ecmwf) is still suggesting that the
longwave trough will close off again...this time in the vcnty of
eastern Pennsylvania. This scenario could enable synoptic moisture
to back in across the Eastern Lake Ontario for Thursday and Thursday
night before ridging finally takes hold of the entire region on
Friday.

&&

Aviation /12z Saturday through Wednesday/...
high pressure will largely maintain VFR conditions through the
period. High clouds will increase this afternoon and tonight,
but still VFR continuing tonight. Some patchy southern tier
valley fog can't be ruled out however a modest southerly flow
will likely provide enough mixing to keep fog from forming.

Outlook...

Sunday and Monday...VFR.
Monday night and Tuesday...MVFR/IFR with occasional rain.
Wednesday...VFR/MVFR with a chance of showers.

&&

Marine...
high pressure ridged across the lower Great Lakes will drift to the
mid-Atlantic coastline by Sunday. Consequently, light to modest
winds and relatively minimal waves will continue through the
weekend. A frontal system is then expected to push though the area
early next week, with strengthening winds and cold advection in its
wake eventually bringing an increasing potential for marine
headlines by either Tuesday or Tuesday night.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...apffel/tma

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